This happens to about 50% of my tabs. (I have over 50 open)
I do not know if this applies to other website, but I would assume it would.

Is this a known issue?

Observed on the steam marketplace (on activation some older tabs will load an item instead of what used to be a search query listing multiple items, page url changed and no back button available).
For example:
The tab url was
http://steamcommunity.com/market/search?q=RPG+Maker+card
Browser was then closed.
Sometimes when I come back to that tab in another session the url changes to one of the listings inside (a page that was visited) with no way of going back to the old url.
In this example
steamcommunity.com/market/listings/753/220700-No%20Transparency?filter=RPG%20Maker%20card
Also note the %20 instead of spaces.
This happens to about 50% of my tabs. (I have over 50 open)
I do not know if this applies to other website, but I would assume it would.
Is this a known issue?

Hi Ansive, in version 27 this is not a known issue yet. In order to reproduce the issue, can you reproduce this in a new profile without the add ons enabled?

If so, we could use the help please file a bug with this important information:

short description

numbered steps to reproduce

what is expected and what actually happens

If you have any questions about this, or would like one of us to help out with the bug please post back with the bug number and one of us would be happy to further investigate when it started to happen.

Looking forward to your reply!

Hi Ansive, in version 27 this is not a known issue yet. In order to reproduce the issue, can you reproduce this in a new profile without the add ons enabled?
If so, we could use the help please file a bug with this important information:
# short description
# numbered steps to reproduce
# what is expected and what actually happens
If you have any questions about this, or would like one of us to help out with the bug please post back with the bug number and one of us would be happy to further investigate when it started to happen.
Looking forward to your reply!